Integrated agriculture-aquaculture and the environment

GENERAL CONSIDERATIONS

Food production invariably has environmental effects: occupation
and fragmentation of former natural habitats; reduction of the abundance of
diversity of wildlife; and, changes in soil water and landscape quality. Most
integrated agriculture-aquaculture systems use low levels of inputs and fall
within the type of aquaculture called semi-intensive. This means less reliance
on heavy feed and fertilized inputs, lower densities of farmed organisms and,
therefore, less chances of causing serious pollution and disease risks than more
intensive, feedlot-type systems. This is important as it is the high output of
the foodstuffs necessary for intensive feedlot systems that create environmental
pollution. Semi-intensive systems in synergy with agriculture
(crop-livestock-fish integrated farming) capitalize on in situ, vitamin and
protein rich natural aquatic feeds, which obviate the need for expensive feed
components.

Semi-intensive freshwater ponds usually have few environmental
effects other than their occupation of former natural habitats. In the tropics,
where there is fast turnover of organic waste loading, their effluents and
excavated muds usually enhance the productivity of adjacent waters and lands and
avoid over enrichment.

Special care is needed, however, where pond and dike
construction may disturb acid sulfate subsoils and where water table changes may
uplift subsurface salts. Moreover, saltwater intrusion from coastal ponds may
poison soils and freshwater aquifers. The use of chemicals in semi-intensive
aquaculture is usually limited, but farmers should always take great care when
using antibiotics, hormones and other drugs and should follow the instructions
very closely. Seek professional advice from veterinarians or fish culture
specialist and be aware that many drugs are persistent in the environment.

CHOICE OF FISH SPECIES

The aquatic medium is shared by many users and supports diverse
fauna and flora. As aquaculturists develop better domesticated breeds,
international demand for these will increase. This means increased transfers of
exotic breeds, as has been of immense benefit for crop and livestock farming.
However, cultured aquatic organisms often escape and form feral populations
which may: (1) displace or interbreed with wild stocks, thereby threatening
natural genetic resources; (2) disrupt natural habitats by causing proliferation
or clearance of vegetation or increasing turbidity (benthic foraging); and, (3)
introduce aquatic pathogens, predators and bests inadvertently.

Development agencies and farmers must weigh the benefits of
using exotic breeds against possible environmental consequences. Development
projects and farmers often try exotic breeds without thorough appraisal of the
possible consequences. Such irresponsible experiments may have far-reaching
consequences; loss or damage to habitats and genetic resources of wide
importance. This damage may last forever. Codas of practice to avoid this have
recently been developed, but aquaculture development still lags behind
agriculture in recognition of the risks of transfers and international
application of these safeguards.

The only general guidelines here are: (1) use native species and
breeds developed by local or national programs wherever possible; and, (2) if
the introduction of other species or breeds need to be considered, seek
professional advice on how to assess the possible consequences and comply with
the laws and Codes of Practice that have been developed for the good of all
present and future farmers.

PUBLIC HEALTH

Integrated agriculture-aquaculture generally has no special
health risks significantly greater than agriculture, but freshwater ponds may
assist the spread of waterborne diseases. They can harbor the intermediate hosts
of parasitic worms, such as bilharzia, and can be breeding sites for mosquitoes.
Such problems are minimized by maintaining weed-free, well-stocked ponds. In
fact, many species of fish eat and control mosquito larvaes but snail control by
fish is not usually possible.

On the positive side, many of the pathogens and parasites that
contaminate fish produce from livestock excrete-fed ponds are eliminated by a
well-fertilized pond environment, as in sewage oxidation ponds. Problems of
pesticide accumulation in ricefield fish are diminishing because of the
increased use of integrated pest management programs employing natural
substances and predators.

The risk of accumulation of heavy metals from livestock feeds in
manured pond sediments and fish is slight and applies more to intensive systems.
The same probably applies to pathways for aflatoxins (poisons that develop from
fungi in badly stored feeds) but this has been little studied.

Sewage-fish culture is controversial because of assumed health
risks to farm workers and fish consumers. However, these may be slight compared
to the nutritional benefits provided that postharvest handling of the fish is
hygienic (with particular attention to not rupturing the gut and allowing its
contents to make contact with fish flesh). Such produce must also be
well-cooked.

There are no general guidelines on how to minimize these risks
other than to be aware of which waterborne diseases are present in any given
locality and to assess whether the establishment and operation of ponds
significantly adds to the risks of contraction by farm workers, fish handlers
and consumers.